The present invention relates to a color developer composition which is designed to be used with recording systems which employ colorless electron donating materials to form images.
Recording materials utilizing developer materials to produce colored images from colorless or substantially colorless electron donating materials are well-known. Specific examples of such recording materials include pressure sensitive carbonless copying paper, heat-sensitive recording paper, electrothermographic recording paper, Cycolor(copyright) photographic materials and the like. They are described in more detail in U.S. Pat. Nos. 2,712,507; 2,730,456; 2,730,457; 3,418,250; 3,432,327; 3,981,821; 3,993,831; 3,996,156; 3,996,405 and 4,000,087. These papers include a developer sheet (also referred to as a CF (coated front) sheet) comprising a substrate coated with an electron acceptor which reacts with a leuco dye transferred to the surface of the developer sheet to form an image thereon.
Much research has been directed to developing new and improved developers for use in the aforementioned recording materials. Representative examples of the developers that have been used include phenol derivatives and phenolic resins, biphenols, methylene bisdiphenols, phenol-formaldehyde novolak resins, metal processed novolak resins, salicylic acid derivatives and salts. See U.S. Pat. No. 3,934,070 to Kimura teaching salicyclic acid derivatives; U.S. Pat. No. 3,244,550 to Farnham teaching biphenols, diphenols, and resinous products containing them, and U.S. Pat. No. 3,244,549 to Farnham teaching phenol derivatives. Representative examples of phenol-formaldehyde condensates previously used in the art are described in numerous patents, including U.S. Pat. No. 3,672,935. Among color developers, phenol-formaldehyde condensates have been widely used because they exhibit excellent color development, good coating properties (rheology) and good water resistance. However, phenolic resins are somewhat colored materials and become even more colored as they are exposed to ambient conditions. Such discoloration is a very undesirable attribute in imaging systems where aesthetic appearance is of extreme importance. Fading of the image when exposed to extreme temperatures and humidity is also an undesirable trait of the currently developer materials. Therefore, it is a principal object of the present invention to provide an improved developer composition for use with recording materials which employ leuco dyes such as carbonless copy paper and photo imaging systems which overcome some of the deficiencies of prior art developers.
The invention is based upon the discovery that molecular sieves and certain alkali metal-containing water insoluble inorganic oxides, when treated with an acid, can be used as a developer for color formers in recording materials.
The developer material of the present invention may be used in any recording system in which a color precursor is reacted with a Lewis acid or electron accepting color developer. Such recording systems include pressure sensitive recording materials like carbonless paper, thermal recording systems and photosensitive systems like the Cycolor(copyright) imaging system described in U.S. Pat. No. 4,399,209 and related patents. It may be used in a self-contained system in which the color precursor and developer are in the same or different layers but present on the same support or it may be used in a transfer system containing a donor or imaging sheet and a developer sheet wherein the donor or imaging sheet contains an image-forming agent capable of reacting with the developer material to form an image. To produce a visible image, the donor or imaging sheet is assembled with the developer sheet and pressure is applied to the sheets to cause transfer of the image-forming agent to the developer sheet. It is particularly envisioned that the developer material of the present invention be coated on a substrate sheet to provide a developer sheet which is then used in association with an imaging sheet containing photosensitive microcapsules containing an image-forming agent. The developer material may also be utilized in a self-contained imaging format.
In accordance with the present invention, a new color developer has been discovered which overcomes many of the drawbacks of the currently used developers.
In one embodiment of the invention, the developer is an acid-treated, alkali metal-modified, inorganic oxide such as silicate, aluminate, borate, borosilicate, phosphate, sulfate, silicon oxide, etc. A typical example of these developers are compounds of the general formula:
Lw+aMy+b(XpOn)zxe2x88x92c 
where L is lithium, sodium, potassium or hydrogen; M is zinc, magnesium or calcium; X is silicon, boron, phosphorus, aluminum, sulfur, titanium or tin; O is oxygen; n is 3 to 25 and p is 1 to 6; and each of w, y and z represents a numeral wherein w(a)+y(b)=z(c) such that the compound is electronically neutral. The general formula is a simplified definition of the compounds. More complex materials are possible because of the tendency of some of the anion forming atoms X to create condensed oxides. Examples of oxide anion structures include (Si3O9)xe2x88x926, (Si4O12)xe2x88x928, (Si8O24)xe2x88x9216, (Si2O5)xe2x88x922, (Si6O17)xe2x88x924, (B2O5)xe2x88x924, (B3O6)xe2x88x923, (P2O7)xe2x88x924, (P3O10)xe2x88x925, (P3O9)xe2x88x923, (S2O6)xe2x88x922 etc.
In another embodiment of the invention, the developer is an acid-treated molecular sieve. Molecular sieves typically comprise a variety of compositions such as silicates, aluminosilicates, aluminophosphates, transitional aluminates, and the like. The inorganic oxide and molecular siene should be essentially water insoluble, i.e., less than 1% soluble in water.
The alkali metal-modified inorganic oxides can be prepared by a process which typically consists of heating the reactants together in air in a temperature range of about 200 to 1200xc2x0 C. for several hours, the temperature used being dependent on the nature of the reactants. After this reaction is complete an acid treatment as discussed later is performed on the reaction product.
A hydrothermal crystallization process is used for preparing the molecular sieves.
This process typically involves of mixing the reactants in a solvent, usually water, and then heating the mixture in a closed reactor at 100 to 300xc2x0 C. for several hours. This reaction is typically carried out in the presence of a templating agent, which provides a specific structure. Following the completion of this reaction, the product is treated with acid. This treatment is followed by a calcining operation. A variety of templates have been used to synthesize molecular sieves from molecular sieve precursors such as the silicate, aluminosilicate, and borosilicate family. Preferably, the molecular sieve precursor is a silicate such as tetraethylorthosilicate (TEOS), tetramethylammonium silicate, tetraethylammonium silicate, etc. Molecular sieves are prepared by crystallization in an aqueous reaction mixture containing an inorganic templating agent such as a nitrogen-containing organo-cation. By varying the synthesis conditions and the composition of the reaction mixture, different zeolites can be formed. The role of templating agents in the preparation of molecular sieves is well known. The positive charge of the organocation templating species is believed to interact with the negatively charged silicate subunits, resulting in the crystallization of the resultant molecular sieve. The organic cation also greatly affects the characteristics of the gel. These effects can range from modifying the gel pH to altering the interactions of the various components via changes in hydration (and thus solubilities of reagents) and other physical properties of the gel.
It has been observed that many of the organocations which have been used as templates for zeolite synthesis are conformationally flexible. These molecules can adopt many conformations in aqueous solution, therefore several templates can give rise to a particular crystalline product. Rollmann and Valyocsik, Zeolites 5, 123 (1985) describe how varying the chain length for a series of alpha, omega-linear diamines resulted in different intermediate-pore products. It has also been reported by M. D. Shannon et al., Nature 353, 417-420 (1991) that three different products which have related framework topologies, can be formed from three linear bis-quaternary ammonium templates of varying chain lengths. Altering the structure of a conformationally rigid organic molecule can also lead to a change in the zeolite obtained, presumably due to the differing steric demands of each template. S. I. Zones, Zeolites 9, 458.467 (1989) reported that in switching from 1,3-dimethylimidazolium hydroxide to 1,3-diisopropylimidazolium hydroxide as template, using the same starting gel (SiO2/Al2O3=100), the former directs toward formation of ZSM-22 whereas the latter affords ZSM-23.
Crystalline zeolitic molecular sieves prepared by hydrothermal crystallization from reaction mixtures containing organic templating agents can, in general, be prepared in forms more highly siliceous than those which are synthesized in the absence of the organic reagents. It has been proposed that the crystallization mechanisms are different. In the case of the low-silica species, the mechanism involves the formation of stabilized metal cation aluminosilicate complexes and is controlled largely by the aluminate and aluminosilicate solution chemistry. In the case of the highly siliceous molecular sieves, a true templating or clathration mechanism is involved in which the organic reagent, typically an alkylammonium cation, forms complexes with silica via hydrogen bonding interactions. These complexes template or cause replication of the structure via stereo-specific hydrogen bonding interaction of the quaternary ammonium cation with the framework oxygens. Whatever the synthesis mechanism, the templated crystal structures in many instances can be directly synthesized over a very wide range of silica alumina (SiO2/Al2O3) ratios. At the extreme upper end of the range, the compositions are essentially silica polymorphs containing no AlO2 tetrahedra in their framework structure. Those highly siliceous molecular sieves, particularly those having SiO2/Al2O3 molar ratios of 200 or greater, are highly hydrophobic and strongly organophilic. As such, they have found extensive use in molecular sieve separations involving organic substrates, particularly those in which water vapor cannot be entirely excluded from contacting the adsorbent.
In accordance with the invention, the water insoluble alkali metal-modified inorganic oxides and the molecular sieves are treated with a Lewis acid. The acid enhances the developing ability of the molecular sieve or inorganic oxide. Preferably, the acid is a Lewis acid such as aluminum halides, zinc halides, transition metal halides, tin halides, boron halides, borates, sulfur trioxide, etc. Mixtures of the above Lewis acids are also useful in treating the alkali metal-modified inorganic oxide and molecular sieve materials. The preferred Lewis acids include AlCl3, ZnCl2, MgCl2, SnCl4 and mixtures thereof. Other acids such as HNO3 have been used successfully to treat the developer materials of the present invention.
The mechanism whereby the acid enhances the developing ability of the inorganic oxide or molecular sieve is not entirely clear. The Lewis acid cation may substitute for other cations in the oxide or sieve, or the Lewis acid may simply be physically absorbed within the oxide or molecular sieve. The treatment of the inorganic oxide or sieve is carried out by mixing the inorganic oxide or sieve with a solution containing about 10 to 20% by weight of the Lewis acid, allowing the mixture to stand for a suitable period of time, e.g., 1 to 2 hours, decanting the water, and drying in the case of the oxide or drying and calcining in the case of the sieve. Depending upon the nature of the oxide and the Lewis acid, the mixture may gel in which case there may not be water to decant. The concentration of the Lewis acid solution and the time the inorganic oxide or sieve stand in the acid can be adjusted to control the acidity of the acid treated product such that the product provides the desired reactivity with the color former and yields an image with good color density.
The developer materials of the present invention can be used alone, combined with each other, or in combination with other developer materials conventionally employed in carbonless paper. Examples of conventional developers with which the developer of the invention may be combined are clay minerals, e.g., acid clay, active clay, attapulgite, etc.; organic acids such as tannic acid, gallic acid, propyl gallate, etc.; acid polymers such as phenol-formaldehyde resins, phenol acetylene condensation resins, condensates between an organic carboxylic acid having at least one hydroxy group and formaldehyde, etc.; metal salts or aromatic carboxylic acids such as zinc salicylate, tin salicylate, zinc 2-hydroxy naphthoate, zinc 3,5 di-tert butyl salicylate, oil soluble metal salts of phenol-formaldehyde novolak resins (e.g., see U.S. Pat. Nos. 3,672,935; 3,732,120 and 3,737,410) such as zinc modified, oil soluble phenol-formaldehyde resin as disclosed in U.S. Pat. No. 3,732,120), zinc carbonate etc. and mixtures thereof.
To produce a developer sheet using the developer material of the present invention, the developer material, typically ground to a particle size of about 2 to about 10 microns, is dispersed in a coating liquid, for example water containing a small amount of a binder, and coated onto a support. The developer coating liquid is applied to the surface of the support using methods known in the art. For example, the developer layer may be formed by applying a coating composition on a support by air-knife coating, pure blade coating, rod blade coating, short dwell coating, curtain coating or die coating. As the support, there may be used paper, plastic film, synthetic paper, non-woven fabric and the like. The amount of the coating composition is not particularly limited, but is generally within the range of about 1 to 20 g/m2 and, preferably about 2 to 10 g/mc dry weight. Due to the low viscosity of the coating formulation, high levels of solids may be added to the dispersion coating solvent. Levels of solids ranging between about 40 to about 70% may be achieved in accordance with the present invention.
A small amount of a binder is usually used to bind the color developer to a support such as paper or PET film. The binder employed may be a natural binder, a synthetic binder or a combination thereof. Illustrative examples of such binders include water-soluble polymers such as starches, e.g., oxidized starch, enzyme-modified starch, cation-modified starch, esterified starch and etherified starch; cellulose derivatives, e.g., methyl cellulose, ethyl cellulose, carboxymethyl cellulose, methoxy cellulose and hydroxyethyl cellulose; polyvinyl alcohols, e.g., completely or partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol and acetoacetyl-modified polyvinyl alcohol; sodium salt of polyacrylic acid; polyacrylamide; polyvinylpyrrolidone; acrylic acid amide-acrylic ester copolymer; acrylic acid amide-acrylic ester-methacrylic acid copolymer; alkali salt of styrene-maleic anhydride copolymer; alkali salt of styrene-acrylic acid copolymer; alkali salt of ethylene-acrylic acid copolymer; alkali salt of isobutylene-maleic anhydride copolymer; sodium alginate; gelatin; casein; gum arabic; urea resins and melamine resin; and latexes such as polyvinylacetate latex, polyurethane latex, polyacrylic acid latex, polyacrylic ester latex, polybutymethacrylate latex, styrene-butadiene copolymer latex, vinyl chloride-vinyl acetate copolymer latex, etylene-vinyl acetate copolymer latex and styrene-butadiene-acrylate latex, butadiene copolymers, vinylidene chloride copolymers, carboxylated styrene-alkylalcohol copolymers, latex, maleic anhydride-styrene copolymer, etc. It is to be understood that all binders well known as film-forming materials can be used in this capacity. Typically, the binder is used in an amount of about 2 to 15% by weight and preferably about 5 to 10% by weight. Other conventional additives such as surfactants, ultraviolet absorbers, antioxidants, plasticizers, hardeners, etc. may be employed in carrying out the invention.
Further, for the purpose of increasing color developing ability and light resistance, an inorganic pigment may be added to the color developer. The inorganic pigment comprises aluminum silicate, zinc silicate, lead silicate, tin silicate, colloidal hydrated aluminum silicate, zeolite, bentonite, kaolinite active clay, acid clay, talc and the like. The amount of inorganic pigment employed is not critical, for example, more than 1 party by weight, preferably 10 to 1000 parts by weight per 100 parts by weight of the metal salt of polymer may be used.
As indicated above, the developer of the present invention can be used in association with any transfer image-forming system. For example, the present invention is particularly useful for preparing a carbonless manifold form. Carbonless paper is widely used in the forms industry. A typical carbonless form is made up of one sheet, known as a CB sheet, which is the first page of the form, and a second sheet, known as a CF sheet, which is the back page of the form. Where a form having more than two sheets is desired, as in the case where more than one copy is required, one or more sheets known as CFB sheets may be placed between the CF and the CB sheet. A CB sheet consists of a sheet of paper having a layer of microcapsules containing a color former coated on its back side, hence the designation CB or xe2x80x9ccoated back.xe2x80x9d A CF sheet consists of a sheet of paper carrying a layer of a developer material on its front side or xe2x80x9ccoated frontxe2x80x9d which reacts with the color former to produce a colored mark. A CFB sheet is coated on its front and back sides. The front is coated with developer and the back is coated with microcapsules. The manifold carbonless forms will usually comprise from about 2 to about 10 individual sheets and preferably from about 2 to about 4 individual sheets per form. To produce a visible image using the developer sheet of the present invention, the developer is brought into contact with an electron donating chromogenic color-forming agent. The color-forming agent is typically maintained in pressure rupturable microcapsules in a manner well known in the art.
Preferably the developer material of the present invention is used in the photosensitive imaging system described in U.S. Pat. No. 4,399,209 and others.
The invention is illustrated in more detail by the following non-limiting Example.